AI Research Engineer: Agent Systems & Evaluation

United States Digital Space LLC; Greater London; Hybrid; GBP 90,000 - 130,000; Full time

Benefits offered by this job

Hybrid work model

King's Cross office

Pet friendly office

Team lunches

Drinks and socials

Job summary

Tessl, the AI native development startup in London, is hiring a Research Engineer to join the AI Research (AIR) team. You’ll work on the components that shape how agent harnesses orchestrate model behavior, how we evaluate what’s working, and how production traces translate into the next improvements.

We expect 4+ years shipping AI/ML products, hands-on with LLMs and agentic systems, plus deep curiosity about agents and how software is built. Hybrid work from our King’s Cross office.

Qualifications

• Essential 4+ years shipping AI/ML products in a startup or applied industry setting, with recent hands-on experience with LLMs and agentic systems.
• Demonstrated depth in at least one of the four skill areas above.
• Strong product and customer instincts: comfort joining customer calls, watching session recordings, and letting real workflows shape what you work on.
• Sharp evaluation judgement: benchmarks where they exist, vibes and quick prototypes where they don't, and the taste to know which is appropriate.
• Experience building datasets for evaluation or training, including the pipeline work that goes with it.
• Deeply curious about agents and excited about reshaping how software is built.
• A Masters or PhD in a relevant computational field.
• Direct experience with coding agents or code-generation systems.
• Background in RL, bandits, or other outer-loop optimisation frameworks applied to LLMs.
• Experience building synthetic data, dataset infrastructure, or internal tooling that other engineers actually used.
• A project you can show us (GitHub links welcome) and a thoughtful answer to "Why Tessl?"

Responsibilities

• Sit in on a customer session, understand how their agents are failing, design an eval that captures it, and drive a fix through to shipped improvement.
• Close a piece of the outer loop end to end: production signal in, dataset out, eval scored, harness change shipped, metric moved.
• Own a slice of our eval infrastructure: dataset curation, harness configuration, runner, analysis, and the comms back to engineering.
• Prototype a new harness or context configuration and measure whether it actually moves the needle on real customer tasks.
• Dig through pages of agent traces, build the tooling you need to make sense of them, and brief the team on what you found.
• Partner with product and engineering on near-term shipping problems by bringing research rigour.
• Pull a recent paper apart, work out what's actually transferable to our platform, and turn it into a concrete experiment.

Skills

LLMs

Agentic systems

Product instincts

Customer instincts

Evaluation judgement

Datasets for evaluation

Experiment prototyping

Education

Masters or PhD in a relevant computational field

Job description

Tessl, the AI native development startup in London, is hiring a Research Engineer to join the AI Research (AIR) team. You’ll work on the components that shape how agent harnesses orchestrate model behavior, how we evaluate what’s working, and how production traces translate into the next improvements.

We expect 4+ years shipping AI/ML products, hands-on with LLMs and agentic systems, plus deep curiosity about agents and how software is built. Hybrid work from our King’s Cross office.